Acoustic wave device and method for manufacturing same

ABSTRACT

An SAW device ( 1 ) has a piezoelectric substrate ( 3 ) propagating acoustic waves, and a comb-shaped electrode ( 6 ) arranged on a first surface ( 3   a ) of the piezoelectric substrate ( 3 ). The SAW device ( 1 ) has a columnar terminal ( 15 ) located on the first surface ( 3   a ) and electrically connected to the comb-shaped electrode ( 6 ), and a cover member ( 9 ) covering a side surface of the terminal ( 15 ). The terminal ( 15 ) comprises, in a first region in the direction of height thereof, a larger diameter on the side of the first surface ( 3   a ) compared with the diameter on the side opposite to the first surface ( 3   a ).

CROSS-REFERENCE TO THE RELATED APPLICATIONS

The present application is a national stage of international applicationNo. PCT/JP2009/069802, filed on Nov. 24, 2009, and claims the benefit ofpriority under 35 USC 119 to Japanese Patent Application No.2008-304900, filed on Nov. 28, 2008 and the entire contents of all ofwhich are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to acoustic wave devices such as a surfaceacoustic wave (SAW) device, a film bulk acoustic resonator (FBAR), orthe like and a method for manufacturing the same.

BACKGROUND ART

An acoustic wave device of a so-called “wafer level package” for thepurpose of reduction of size etc. is known. In this acoustic wavedevice, an excitation electrode arranged on the surface of the elementsubstrate is sealed by a resin while being accommodated in a vibrationspace. In other words, the excitation electrode is covered by a covermember. Further, a columnar terminal connected to the excitationelectrode is vertically provided on the surface of the elementsubstrate. The columnar terminal is exposed at its front end sideportion (portion on the side opposite to the surface of the elementsubstrate) from the cover member. Further, the acoustic wave device ismounted on a circuit board by soldering of the exposed portion of thecolumnar terminal to the circuit board and so on. Patent Literature 1discloses an elastic wave device in which a columnar terminal is formedin a taper (inverse taper) where the diameter of the front end sideportion becomes larger than that of the root side portion (portion ofthe element substrate on the side by the surface).

An acoustic wave device is sometimes subjected to a force in a directionmaking it move from the circuit board due to gravity, impact upondropping, and so on. At this time, since the terminal of the acousticwave device is fixed at its front end side portion to the circuit board,force ends up being applied in a direction pulling it out from the covermember.

Accordingly, preferably an acoustic wave device able to restrain theterminal from being pulled out from the cover member and a method formanufacturing the same are provided.

-   Patent Literature 1: Japanese Patent Publication (A) No. 2007-208665

SUMMARY OF INVENTION

An acoustic wave device according to an embodiment of the presentinvention has a substrate configured to propagate acoustic waves; aterminal with a pillar-shape located on a surface of the substrate andcomprising a first region in a direction of height thereof with across-sectional area of surface side larger than the a cross-sectionalarea of the side opposite to that surface; an excitation electrodelocated on the surface of the substrate and electrically connected tothe terminal; and a cover member covering a side surface of the firstregion of the terminal.

A method for manufacturing an acoustic wave device according to anembodiment of the present invention has a step of arranging anexcitation electrode on a surface of a substrate which propagatesacoustic waves; a step of forming a terminal with a pillar-shape whichis electrically connected to the excitation electrode and which islocated on the surface and which comprises a first region in a heightdirection thereof with a cross-sectional area of the surface side largerthan the a cross-sectional area of the side opposite to that surface;and a step of forming a cover member which forms a hollow vibrationspace above the excitation electrode and covers the side surface of theterminal.

Effects of Invention

According to the above acoustic wave device, the terminal of theacoustic wave device can be restrained from being pulled out of thecover member.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1 A and B are a schematic plan view and cross-sectional viewshowing a SAW device according to an embodiment of the presentinvention.

FIGS. 2 A to D are schematic cross-sectional views for explaining amethod for manufacturing the SAW device of FIG. 1A and FIG. 1B.

FIGS. 3 A to D are schematic cross-sectional views continuing from FIG.2D.

FIGS. 4 A and B are schematic cross-sectional views continuing from FIG.3D.

FIGS. 5 A to C are schematic cross-sectional views showing SAW devicesaccording to first to third modifications of the present invention.

FIGS. 6 A to D are schematic cross-sectional views for explaining amethod for manufacturing a SAW device according to a fourth modificationof the present invention.

FIG. 7 A schematic cross-sectional view showing a SAW device accordingto a fifth modification of the present invention.

DESCRIPTION OF EMBODIMENTS Structure of SAW Device

FIG. 1A is a schematic plan view showing a SAW device 1 according to anembodiment of the present invention. FIG. 1B is a schematiccross-sectional view taken along the Ib-Ib line in FIG. 1A. Note that,FIGS. 1A and 1B schematically show the SAW device 1 for facilitatingunderstanding of the SAW device 1. In execution, the sizes, numbers,shapes etc. of parts of the SAW device 1 may be suitably set as well.

The SAW device 1 has a piezoelectric substrate 3, a SAW element 5arranged on the piezoelectric substrate 3, a protective layer 7 andcover member 9 for protecting the SAW element 5, and a connection-useconductor 11, a connection strengthening layer 13 and a terminal 15 forelectrically connecting the SAW element 5 with a not shown electroniccircuit.

The piezoelectric substrate 3 is a block-shaped single crystal substratehaving a piezoelectric property such as a lithium tantalite singlecrystal, a lithium niobate single crystal or the like. The piezoelectricsubstrate 3 has a first surface 3 a and a second surface 3 b on the backsurface side of that. Note that, in FIG. 1A and FIG. 1B, a case where anelectrode etc. are arranged on only the first surface 3 a isexemplified. However, an electrode etc. may be arranged on the secondsurface 3 b as well.

The SAW element 5 has a plurality of pairs of comb-shaped electrodes(IDT electrodes) 6 formed on the first surface 3 a of the piezoelectricsubstrate 3. Each comb-shaped electrode 6 has a plurality of electrodefingers extending in a direction perpendicular to a direction ofpropagation of the SAW on the piezoelectric substrate 3 (left-rightdirection on the sheet surface of FIG. 1A and FIG. 1B). Each pair ofcomb-shaped electrodes 6 are formed so that their electrode fingers meshwith each other.

Note that, FIG. 1A and FIG. 1B are schematic views, therefore show onlya pair of comb-shaped electrodes 6 comprised of a comb-shaped electrode6 having two electrode fingers and a comb-shaped electrode 6 havingthree electrode fingers. In actuality, several pairs of comb-shapedelectrodes having numbers of electrode fingers larger than those may beprovided as well. Further, a ladder type SAW filter or double mode SAWresonator filter etc. may be configured by connection of a plurality ofSAW elements 5 by serial connection, parallel connection, or anothermethod. At both ends of the SAW element 5, reflectors (may be grasped asportions of the SAW element 5 as well) having comb-shaped electrodes maybe provided as well. The SAW element 5 is formed by, for example, an Alalloy such as an Al—Cu alloy or the like.

The protective layer 7 covers the SAW element 5 and contributes toprevention of oxidation etc. of the SAW element 5. The protective layer7 is formed by a material which has an insulating property and is lightenough in weight to an extent that it does not exert an influence uponthe propagation of a SAW. For example, the protective layer 7 is made ofsilicon oxide, silicon nitride, silicone, or the like.

The cover member 9 covers the SAW element 5 from the top of theprotective layer 7. Note, the cover member 9 forms a vibration space 17above the SAW element 5 for making propagation of SAW easy. In otherwords, the cover member 9 has a wall section 19 forming an inner wall 19a of the vibration space 17 and has a lid 21 forming a ceiling 21 a ofthe vibration space 17.

The thickness of the layer forming the wall section 19 (height of thewall section 19 from the first surface 3 a) and the thickness of the lid21 may be suitably set. For example, these thicknesses are severalmicrometers to 30 μm. The wall section 19 and lid 21 are formed to forexample substantially equal thicknesses.

The wall section 19 and the lid 21 may be formed by separate materialsor formed by different materials. The wall section 19 and lid 21 areformed by, for example, a photocurable material which is cured byirradiating UV-rays, visible rays, or other light. In other words, thewall section 19 and lid 21 are formed by negative type photoresists. Thephotocurable material is for example a resin which is cured by radicalpolymerization of acrylic groups, methacrylic groups, or the like. Morespecifically, this is a urethane acrylate-based, polyesteracrylate-based, or epoxy acrylate-based resin.

In the vibration space 17, as shown in FIG. 1B, the cross-section isformed to a substantially rectangular state. The corners at the lid 21side are formed by curved surfaces. In other words, the inner wall 19 aconfiguring the vibration space 17 is inclined inwardly the further fromthe first surface 3 a of the substrate 3. The planar shape of thevibration space 17 (shape in the plan view of the first surface 3 a) maybe suitably set. For example, the planar shape of the vibration space 17is formed to a rectangular shape. The size of the vibration space 17 maybe suitably set.

The connection-use conductor 11 is for connecting the SAW element 5 andthe terminal 15. The connection-use conductor 11 is for example formedon the first surface 3 a of the piezoelectric substrate 3 in the sameway as the SAW element 5. The connection-use conductor 11 is formed onthe first surface 3 a in a suitable pattern for connection to the SAWelement 5 although this is not particularly shown. Further, theconnection-use conductor 11 is formed so that it has a broadness atleast equivalent to the end face of the terminal 15 on the first surface3 a side at the position where the terminal 15 is arranged. Theconnection-use conductor 11 is formed by for example the same materialas that for the SAW element 5 and is formed to the same thickness asthat of the SAW element 5.

The connection strengthening layer 13 is for reinforcing the relativelythinly formed connection-use conductor 11 and strengthening theconnection of the connection-use conductor 11 with the terminal 15. Theconnection strengthening layer 13 is stacked on the connection-useconductor 11 at the position of arrangement of the terminal 15. Further,the connection strengthening layer 13 is formed to have a broadnessequal to that of the end face of the terminal 15 on the first surface 3a side or more. The connection strengthening layer 13 is for exampleformed so that a thickness of the connection-use conductor 11 and theconnection strengthening layer 13 is substantially equal to a thicknessof the protective layer 7, and the connection strengthening layer 13 isexposed from the protective layer 7. The connection strengthening layer13 is formed by for example chromium or nickel.

The terminal 15 is provided on the connection strengthening layer 13.Accordingly, the terminal 15 is electrically connected through theconnection strengthening layer 13 and connection-use conductor 11 to theSAW element 5. Further, the terminal 15 is formed in a columnar shapeand is vertically provided from the first surface 3 a. Further, thefront end side portion of the terminal 15 is exposed from the covermember 9 so that it can be connected to a not shown circuit board etc.The terminal 15 is formed by for example solder, Cu, Au, or Ni.

The terminal 15 has a first columnar section 23 which forms the rootside portion of the columnar portion and has a side surface which iscovered by the wall section 19, a second columnar section 25 which formsthe front end side portion of the columnar portion and has a sidesurface which is covered by the lid 21, and a land 27 which is exposedfrom the lid 21.

Each of the first columnar section 23 and the second columnar section 25is formed in a taper where its first surface 3 a side has a diameterlarger than the side opposite to the first surface 3 a. In other words,in the terminal 15, in at least a portion (first region) thereof, thecross-sectional area of the first surface 3 a side is made larger thanthe cross-sectional area of the side opposite to the first surface 3 a.Note that, the first columnar section 23 may be grasped as the firstregion or the second columnar section 25 may be grasped as the firstregion. The end face of the first columnar section 23 on the secondcolumnar section 25 side has a diameter smaller than that of the endface of the second columnar section 25 on the first columnar section 23side. A step 29 where the diameter of the side opposite to the firstsurface 3 a is larger than that of the first surface 3 a side is formedat the boundary between the first columnar section 23 and the secondcolumnar section 25.

The first columnar section 23 and the second columnar section 25 are forexample formed to substantially the same sizes and shapes. Morespecifically, in the first columnar section 23 and second columnarsection 25, the sizes and diameters of the end faces on the sidesopposite to the first surface 3 a are substantially the same as eachother. Further, inclinations of the tapered surfaces are substantiallythe same as each other.

The land 27 is for example formed so that its area is broader than thatof the end face of the second columnar section 25 on the side oppositeto the first surface 3 a. The outer peripheral part is stacked on thecover member 9.

Note that the shapes of the first columnar section 23, second columnarsection 25, and land 27 in the plane view of the first surface 3 a maybe suitably set. For example, these shapes are circular. Further, thesizes of the first columnar section 23, second columnar section 25, andland 27 in the plane view of the first surface 3 a are smaller incomparison with the size of the vibration space 17 in the plane view ofthe first surface 3 a. As an example, in the plane view of the firstsurface 3 a, the diameter of the terminal 15 is 100 μm in contrast tothe size 500 μm×500 μm of the vibration space 17.

Method for Manufacturing SAW Device

FIG. 2A to FIG. 4B are schematic cross-sectional views for explainingthe method for manufacturing the SAW device 1.

The method for manufacturing the SAW device 1 substantially includes astep of forming the SAW element 5 (FIG. 2A), a step of forming the covermember 9 (FIG. 2C to FIG. 3D), and a step of forming the terminal 15(FIG. 4A and FIG. 4B). Specifically, these are as follows.

As shown in FIG. 2A, first, on the first surface 3 a of thepiezoelectric substrate 3, the SAW element 5 and connection-useconductor 11 are formed. Specifically, first, a metal layer is formed onthe first surface 3 a of the piezoelectric substrate 3 a by thin filmforming method such as sputtering method, vapor deposition method, CVD(chemical vapor deposition) or the like. Next, the metal layer ispatterned by photolithography using a reduced projection exposureapparatus (stepper) and RIE (reactive ion etching) apparatus or theother method. Accordingly, the SAW element 5 and connection-useconductor 11 are formed.

After the SAW element 5 and connection-use conductor 11 are formed, asshown in FIG. 2B, the protective layer 7 and connection strengtheninglayer 13 are formed. Either of the protective layer 7 or connectionstrengthening layer 13 may be formed first. For example, first, a thinfilm which becomes the protective layer 7 is formed to cover the top ofthe SAW element 5 and connection-use conductor 11 by thin film formingmethod such as CVD method, vapor deposition method or the like. Next, aportion of the thin film is removed by photolithography so that aportion in the connection-use conductor 11 at the position where theterminal 15 is arranged is exposed. Accordingly, the protective layer 7is formed. Next, a metal layer is formed on the exposed portion of theconnection-use conductor 11 and the protective layer 7 by the vapordeposition method or the like, and the metal layer on the protectivelayer 7 is removed by photolithography or the like. Accordingly, theconnection strengthening layer 13 is formed.

When the protective layer 7 and connection strengthening layer 13 areformed, as shown in FIG. 2C to FIG. 3A, the wall section 19 is formed.

Specifically, first, as shown in FIG. 2C, a wall section-forming layer31 configuring the wall section 19 is formed on the protective layer 7and connection strengthening layer 13. The wall section-forming layer 31is for example formed by adhesion of a film formed by a negativephotoresist.

Next, as shown in FIG. 2B, light such as UV-rays or the like isirradiated to the wall section-forming layer 31 through a photomask 33.Namely, exposure process is executed. The photomask 33 is for exampleconfigured by the formation of a blocking layer 37 on a transparentsubstrate 35. The blocking layer 37 is arranged at the positioncorresponding to the position where the wall section-forming layer 31must be removed. Namely, it is arranged at the position corresponding tothe arrangement position of the vibration space 17 and the arrangementposition of the terminal 15. Note that, the exposure may be projectionexposure, proximity exposure, or contact exposure.

After that, as shown in FIG. 3A, development process is executed. In thewall section-forming layer 31, portions which were irradiated by lightare left while portions which were not irradiated by light are removed.Accordingly, in the wall section-forming layer 31, an opening 39 whichbecomes the vibration space 17 and a first hole portion 41 in which thefirst columnar section 23 arranged are formed. Namely, the wall section19 is formed.

Here, at the edge portion of the region irradiated by light in the wallsection-forming layer 31, the irradiated light is diffused to the regionwhich is not irradiated by the light in the wall section-forming layer31, therefore sufficient light does not reach the first surface 3 aside. Accordingly, the first surface 3 a side of the edge portion of theregion which is irradiated by light in the wall section-forming layer 31is not fully cured and removed. As a result, the first hole portion 41is formed in a taper (forward taper) having a diameter becoming largertoward the first surface 3 a side.

In the same way, the opening 39 is formed in a taper (forward taper)having a diameter becoming larger toward the first surface 3 a side.Note that, light diffuses easier in the region in which the opening 39is formed in comparison with the region in which the first hole portion41 is formed because the opening 39 is larger than the first holeportion 41 and its edge portion is straight in a plane view etc.Accordingly, in the cross-sectional view, the first hole portion 41 istapered as a whole. In contrast, in the opening 39, only the portion onthe side opposite to the first surface 3 a side becomes tapered.Further, in the cross-sectional view, the tapered surface of the opening39 is shaped so that the tapered surface of the first hole portion 41 isvertically compressed, therefore the curvature becomes larger incomparison with the tapered surface of the first hole portion 41, so itbecomes easier to be recognized as a curved surface.

After the first hole portion 41 and opening 39 are formed, as shown inFIG. 3B to FIG. 3D, the lid 21 is formed.

Specifically, first, as shown in FIG. 3B, on the wall section 19, alid-forming layer 43 for forming the lid 21 is formed. The lid-forminglayer 43 is for example formed by adhesion of a film formed by anegative photoresist. Due to the formation of the lid-forming layer 43,the opening 39 of the wall section 19 (FIG. 3A) is closed, and thevibration space 17 is formed. Note that, preferably the wallsection-forming layer 31 and the lid-forming layer 43 are joined byheating.

Next, as shown in FIG. 3C, light such as UV-rays or the like isirradiated through a photomask 45 to the lid-forming layer 43. Namely,exposure process is executed. The photomask 45 is configured by theformation of a blocking layer 49 on a transparent substrate 47 in thesame way as the photomask 33. The blocking layer 49 is arranged at aposition corresponding to the position where the lid-forming layer 43 isto be removed. Namely, it is arranged at a position corresponding to thearrangement position of the terminal 15. The photomask 45 for example isconfigured by removing, in the photomask 33, a portion corresponding tothe vibration space 17 in the blocking layer 37. Note that, the exposuremay be projection exposure, proximity exposure, or contact exposure.

After that, as shown in FIG. 3D, development process is executed. In thelid-forming layer 43, portions which were irradiated by light are leftwhile portions which were not irradiated by light are removed.Accordingly, in the lid-forming layer 43, a second hole portion 51 inwhich the second columnar section 25 is arranged is formed. Namely, thelid 21 is formed. Due to the formation of the lid 21, the cover member 9is completed by the wall section 19 and lid 21. Note that, the firsthole portion 41 and the second hole portion 51 are connected to form acombined hole 53.

After the cover member 9 is formed, as shown in FIG. 4A and FIG. 4B, theterminal 15 is formed. Specifically, first, as shown in FIG. 4A, aplating-use underlayer 55 and a plating-use resist layer 57 are formed.

The plating-use underlayer 55 is formed to cover the cover member 9.Further, the plating-use underlayer 55 is formed on the bottom surfaceof the combined hole 53 formed by the connection strengthening layer 13and on the inner circumferential surface of the combined hole 53 formedby the cover member 9. The plating-use underlayer 55 is formed by aTi—Cu alloy or the like by for example flash plating as a preferredexample. When the plating-use underlayer 55 is formed by flash plating,it is not necessary to form an line pattern for making current flow inthe plating forming part. Accordingly, reduction of size of the SAWdevice 1 becomes possible.

The plating-use resist layer 57 is formed on the plating-use underlayer55. The plating-use resist layer 57 is formed on the substrate by forexample spin coating or another technique. In the plating-use resistlayer 57, a land-use hole 59 is formed above the combined hole 53. Theland-use hole 59 has a diameter larger than the diameter of the combinedhole 53 and has a depth (thickness of the plating-use resist layer 57)not less than the thickness of the land 27. The land-use hole 59 isformed by for example photolithography.

Next, as shown in FIG. 4B, the plating-use underlayer 55 exposed throughthe land-use hole 59 is plated. Accordingly, metal is filled in thecombined hole 53 and land-use hole 59. Then, the first columnar section23 is formed by the metal filled in the first hole portion 41, thesecond columnar section 25 is formed by the metal filled in the secondhole portion 51, and the land 27 is formed by the metal filled in theland-use hole 59. Note that, in the land-use hole 59, the metal does nothave to be filled up to the surface of the plating-use resist layer 57.The metal may be filled up to a suitable depth of the land-use hole 59.The plating method may be suitably selected, but electroplating ispreferred. This is because electroplating gives a high degree of freedomof the height of the columnar terminal 15, and results in a goodadhesion with the plating-use underlayer 55.

After that, the plating-use resist layer 57 is removed, and the portionin the plating-use underlayer 55 which has not been exposed from theland-use hole 59 is removed. Accordingly, as shown in FIG. 1B, the SAWdevice 1 is formed. Note that, in FIG. 1B, illustration of the remainingportion of the plating-use underlayer 55 is omitted. The plating-useresist layer 57 can be removed by for example organic solvent such asacetone, IPA, or the like or alkali organic solvent such as dimethylsulfoxide or the like. The Cu of the plating-use underlayer 55 can beremoved by for example a mixture of iron (II) chloride or phosphoricacid with a hydrogen peroxide solution. Further, the Ti of theplating-use underlayer 55 can be removed by for example a mixture ofdilute fluoric acid or ammonia with a hydrogen peroxide solution.

Note that, the above steps are realized by a so-called wafer process.Namely, the steps explained above are carried out on a wafer which islater divided into piezoelectric substrates 3. A large number's worth ofthe SAW devices are formed in parallel.

According to the above embodiment, the SAW device 1 has thepiezoelectric substrate 3 for propagating acoustic waves and thecomb-shaped electrodes 6 arranged on the first surface 3 a of thepiezoelectric substrate 3. Further, the SAW device 1 has the columnarterminal 15 which is provided vertically from the first surface 3 a andis electrically connected to the comb-shaped electrodes 6 and has thecover member 9 which forms the hollow vibration space 17 above thecomb-shaped electrode 6 and covers the side surface of the terminal 15.Further, in the terminal 15, in at least a portion in the verticaldirection, the first surface 3 a side has a diameter larger than that ofthe side opposite to the first surface 3 a. Accordingly, when force isapplied to the terminal 15 in a direction pulling the terminal 15 out ofthe cover member 9, the terminal 15 engages with the cover member 9, andpulling the terminal 15 out is restrained. Namely, the durability of theSAW device 1 is improved.

The terminal 15 has a tapered portion (first columnar section 23 andsecond columnar section 25) in which the first surface 3 a side has adiameter larger than that of the side opposite to the first surface 3 a.Accordingly, when force is applied to the terminal 15 in a directionpulling the terminal 15 out of the cover member 9, the terminal 15engages with the cover member 9 over a relatively wide area. As aresult, local application of load to the cover member 9 is suppressed.Then, breakage of the cover member 9 and pullout of the terminal 15 dueto the breakage are suppressed.

The terminal 15 has, as the tapered portion, the first columnar section23 and the second columnar section 25 continuing from the side oppositeto the first surface 3 a in the first columnar section 23. The diameterof the first columnar section 23 at the second columnar section 25 sideis smaller than the diameter of the second columnar section 25 at thefirst columnar section 23 side. Accordingly, while obtaining the sameengagement strength against pullout as that in the later explainedsecond modification (see FIG. 5B), the change of the cross-sectionalarea in the vertical direction at the section parallel to the firstsurface 3 a can be made smaller than that of the second modification. Asa result, the ratio of the maximum cross-sectional area with respect tothe minimum cross-sectional area of the terminal 15 (exerting aninfluence upon the electrical resistance of the terminal 15) can be madesmaller, and the terminal 15 can be reduced in size. Further, when forceis applied to the terminal 15 in a direction pushing against theterminal 15, a portion of that force will be transmitted to the covermember 9, therefore the load of the connection strengthening layer 13can be lightened. As a result, improvement of the durability andreduction of the thickness or elimination of the connectionstrengthening layer 13 are facilitated.

The position of the boundary (step 29) between the first columnarsection 23 and the second columnar section 25 from the first surface 3 acoincides with the position of the ceiling 21 a of the vibration space17 from the first surface 3 a. Accordingly, when force is applied in adirection pushing against the terminal 15, the transmission of thatforce from the step 29 to the lid 21 is suppressed. Consequently,bending of the lid 21 and contact of the ceiling 21 a with the bottomsurface (protective layer 7) of the vibration space 17 are suppressed.On the other hand, the force in the direction of pushing which istransmitted from the step 29 to the wall section 19 is applied to theentire wall section 19 in the height direction from the first surface 3a, so the force which is transmitted to the wall section 19 can bedispersed over a wide range. Further, in the case where the wall section19 and the lid 21 are formed by separate steps (separate layers), ineach layer, a hole (first hole portion 41 or second hole portion 51) maybe formed into simple shape. In other words, it is not necessary to forma hole having a diameter reduced in the middle in the opening direction,so the formation of the combined hole 53 is easy.

An inner wall 19 a and a ceiling 21 a of the vibration space 17 areformed in an arch shape. Accordingly, bending of the lid 21 issuppressed. As a result, for example, the SAW device 1 can be reduced insize by reducing the height of the vibration space 17.

The method for manufacturing the SAW device 1 has a step (FIG. 2A) ofarranging the comb-shaped electrodes 6 on the first surface 3 a of thepiezoelectric substrate 3 for propagating acoustic waves. Further, themanufacturing method has a step (FIG. 4A and FIG. 4B) of forming acolumnar terminal 15 which is electrically connected to the comb-shapedelectrodes 6, is vertically provided from the first surface 3 a, andhas, in at least a portion in the vertical direction, a larger diameteron the first surface 3 a side than that of the side opposite to thefirst surface 3 a. Further, the manufacturing method has a step (FIG. 2Cto FIG. 3D) of forming the hollow vibration space 17 above thecomb-shaped electrodes 6 and forming the cover member 9 covering theside surface of the terminal 15. Accordingly, the SAW device 1restrained from pullout of the terminal 15 is formed.

The step of forming the cover member 9 has a step (FIG. 2C and FIG. 3B)of forming the cover member-forming layer (wall section-forming layer 31and lid-forming layer 43) which becomes the cover member 9. Further, thestep of forming the cover member 9 has a step (FIG. 2D and FIG. 3A andFIG. 3C and FIG. 3D) of forming the combined hole 53 in the covermember-forming layer. In the combined hole 53, in at least a portion ofthe vertical direction of the terminal 15, the first surface 3 a sidehas a diameter larger than that of the side opposite to the firstsurface 3 a. Then, in the step (FIG. 4B) of forming the terminal 15, aconductive material (metal) is filled in the combined hole 53 to formthe terminal 15.

Accordingly, in at least a portion of the vertical direction, theterminal 15 where the first surface 3 a side has a diameter larger thanthat of the side opposite to the first surface 3 a is easily formed. Inaddition, in comparison with the method of formation of the laterexplained fourth modification (see FIG. 6A to FIG. 6D), it is notnecessary to provide a resist layer, which is removed later, for onlyforming the columnar sections of the terminal 15, so the manufacturingmethod is simplified.

In the step of forming the combined hole 53, the combined hole 53 isformed by removal of a portion of the cover member-forming layer (wallsection-forming layer 31 and lid-forming layer 43) by negativephotolithography. Accordingly, by positively utilizing a phenomenonwhich is originally undesirable such as diffusion of light for exposure,it is possible to form a combined hole 53 having a larger diameter onthe first surface 3 a side than that of the side opposite to the firstsurface 3 a in at least a portion of the vertical direction of theterminal 15. As a result, it is not necessary to add a special step formaking the diameter of a portion of the combined hole 53 larger, so themanufacturing method is simplified.

The step of forming the cover member-forming layer has a step (FIG. 2C)of forming the wall section-forming layer 31 which forms the wallsection 19 of the vibration space 17 and a step (FIG. 3B) of forming thelid-forming layer 43 which forms the lid 21 of the vibration space 17 onthe wall section-forming layer 31. The step of forming the combined hole53 has, before the step of forming the lid-forming layer 43, a step(FIG. 2D and FIG. 3A) of removing a portion of the wall section-forminglayer 31 by negative photolithography to form the opening 39 whichbecomes the vibration space 17 and the first hole portion 41. The firsthole portion 41 is the hole which becomes the surface side portion inthe combined hole 53 and has a larger diameter on the first surface 3 aside than that of the side opposite to the first surface 3 a. Further,the step of forming the combined hole 53 has, after the step of formingthe lid-forming layer 43, a step (FIG. 3C and FIG. 3D) of removing aportion of the lid-forming layer 43 by negative photolithography to formthe second hole portion 51. The second hole portion 51 is the hole whichbecomes the portion on the side opposite to the first surface 3 a in thecombined hole 53, has a diameter on the first surface 3 a side enlargedfrom that of the side opposite to the first surface 3 a, and has adiameter on the first surface 3 a side larger than the diameter of thefirst hole portion 41 on the side opposite to the first surface 3 a.

Accordingly, as explained above, the combined hole 53 capable of formingtwo tapered portions (first columnar section 23 and second columnarsection 25) of the terminal 15 having a diameter reduced in a portion inthe opening direction is realized by the formation of the first holeportion 41 and second hole portion 51 having simple shapes.

Note that, in the above embodiment, the SAW device 1 is an example ofthe acoustic wave device of the present invention, the piezoelectricsubstrate 3 is an example of the substrate of the present invention, andthe first surface 3 a is an example of the surface of the substrate ofthe present invention. Further, the comb-shaped electrode 6 is anexample of the excitation electrode of the present invention, the firstcolumnar section 23 is an example of the first tapered portion of thepresent invention, and the second columnar section 25 is an example ofthe second tapered portion of the present invention.

The present invention is not limited to the above embodiment, but may beworked in a variety of ways.

The acoustic wave device is not limited to a SAW device. For example,the acoustic wave device may be a film bulk acoustic resonator. In theacoustic wave device, the protective layer (7) and connectionstrengthening layer (13) may be omitted. Conversely, another suitablelayer may be formed. For example, in the embodiment, a metal layer (flatsheet) which is stacked on the wall section 19 or lid 21 and issupported by the terminal 15 connected to the reference potential may beprovided. In this case, the strength against bending of the lid 21 canbe reinforced by the metal layer.

The terminal is not limited to tapered one. A terminal in which thesurface side has a diameter larger than that of the side opposite to thesurface in at least a portion of the vertical direction may be realizedby a suitable shape.

FIG. 5A is a schematic cross-sectional view showing a terminal 115 ofthe first modification. The terminal 115 has a first columnar section123 vertically provided on the connection strengthening layer 13, asecond columnar section 125 vertically provided on the first columnarsection 123, and a land 27 provided on the second columnar section 125.The first columnar section 123 and the second columnar section 125 areformed in columnar shapes. Further, the diameter of the first columnarsection 123 is larger than the diameter of the second columnar section125.

According to the first modification, in the same way as the embodiment,the terminal 115 engages with a cover member 109 whereby pullout issuppressed. Further, in the wall section 119 and lid 121 of the covermember 109, a hole having a uniform diameter in the opening directionmay be formed, therefore the degree of freedom of selection of a methodof forming a hole increases.

Further, when the terminal has a tapered portion, the number of taperedportions is not limited to two. The number of tapered portions may beone or three or more as well.

FIG. 5B is a schematic cross-sectional view showing a terminal 215 ofthe second modification. The terminal 215 has a columnar section 223vertically provided on the connection strengthening layer 13 and a land27 provided on the columnar section 223. The columnar section 223 is theentire portion of the terminal 15 which has a side surface covered bythe cover member 9. It is formed in a single taper. Note that, in orderto form such a columnar section 223, for example, negativephotolithography may be carried out to make the diameter of the holeformed in the lid 221 smaller than the diameter of the hole formed inthe wall section 219.

According to the second modification, in the same way as the aboveembodiment, the terminal 215 engages with the cover member 209, wherebypullout is suppressed. Further, in the terminal 215 and at the portionof the cover member 209 covering the terminal 215, formation of angleportions is suppressed, so occurrence of stress concentration issuppressed and the durability is improved.

Further, in the terminal, in the entire portion where the side surfaceis covered by the cover member, formation of a taper is not necessary.

FIG. 5C is a schematic cross-sectional view showing a terminal 315 ofthe third modification. The terminal 315 has a first columnar section 23vertically provided on the connection strengthening layer 13, a secondcolumnar section 125 vertically provided on the first columnar section23, and a land 27 provided on the second columnar section 125. The firstcolumnar section 23 is formed in a taper in the same way as theembodiment, while the second columnar section 125 is formed in acolumnar shape in the same way as the first modification.

According to the third modification, in the same way as the aboveembodiment, the terminal 315 engages with a cover member 309 wherebypullout is suppressed. Further, in the lid 121, it is not necessary toform a tapered hole, so the degree of freedom of selection of the methodof forming the hole is high. As a result, it becomes easy to make thematerial forming the wall section 19 and the material forming the lid121 different and so on. Note that, opposite to the third modification,the first columnar section may be formed in a columnar state, while thesecond columnar section may be formed in a taper.

The position of the step (29) formed by the first tapered portion (23)and the second tapered portion (125) from the surface (3 a) does nothave to coincide with the position of the ceiling (21 a) of thevibration space (17) from the surface (3 a). Further, the manufacturingmethod for making the position of the step and the position of theceiling not coincident can be suitably selected as well. For example, inthe above embodiment, the cover member was formed by two photoresistlayer (31, 43), but the cover member may be configured by a plurality ofphotoresist layers of a number larger than the former to form a step ofa taper at a suitable position as well.

In the above embodiment, the step of forming the terminal was carriedout after the step of forming the cover member, but the cover member maybe formed after the step of forming the terminal as well.

FIG. 6A to FIG. 6D are schematic cross-sectional views for explaining amethod for manufacturing a SAW device 401 of a fourth modification. Inthe fourth modification, after the terminal 415 is formed, a covermember 409 (FIG. 6D) is formed. Specifically, this is as follows.

First, as shown in FIG. 6A, on the first surface 3 a of thepiezoelectric substrate 3, an inner-shell section 419 forming avibration space 417 is formed above the SAW element (not shown). Theinner-shell section 419 forms the inner side portion of the cover member409. The inner-shell section 419 is formed by for example aphotosensitive resin.

Next, as shown in FIG. 6B, a terminal-use resist layer 457 having a hole453 formed in it is formed. A terminal 415 is formed by filling aconductive material in the hole 453. The hole 453 and terminal 415 arefor example formed in a taper as a whole in the same way as the secondmodification.

After that, as shown in FIG. 6C, the terminal-use resist layer 457 isremoved. Accordingly, the side surface of the terminal 415 is exposed.

Then, as shown in FIG. 6D, the inner-shell section 419 and the terminal415 are sealed by a resin. The top surface side portion of the sealingresin is ground until the terminal 415 is exposed (up to the positionindicated by a dotted line). By the ground sealing resin, an outer-shellsection 421 forming the outer side portion of the cover member 409 isformed.

Note that when the terminal is formed earlier than the cover member, themethod of forming the terminal is not limited to the method of filling aconductive material in a hole formed in the resist layer. For example,by performing vapor deposition of the metal through masks several timesby using a plurality of masks having transmission holes with diametersdifferent from each other, a terminal having a diameter enlarged atsuitable positions may be formed.

When forming a hole in the cover member etc. and filling a conductivematerial in the hole to form a terminal, the formation of the hole isnot limited to formation using photolithography. For example, the holemay be formed by ablation by a laser beam. Note that, in this case, thetapered surface can be formed by for example making the irradiationangle of the laser beam incline relative to the surface of thesubstrate.

Further, when the hole in which a conductive material is to be filled toform the terminal is formed by photolithography, the formation of thetapered surface is not limited to one utilizing diffusion of light innegative photolithography. For example, in positive or negativephotolithography, it is possible to form the tapered surface byirradiating the light at an angle relative to the surface of thesubstrate. Further, in negative photolithography, it is possible to forma tapered hole in which the diameter of the surface side is enlarged byirradiating the light at the resist while reducing the diameter of thelight by the reduced projection system.

In the above embodiment, in the tapered portion of the terminal, thesurface side was enlarged in diameter compared with that of the sideopposite to the surface. However, the tapered portion of the terminalmay be formed so that the side opposite to the surface is enlarged indiameter compared with that of the surface side as well.

FIG. 7 is a schematic cross-sectional view showing a SAW device 501according to a fifth modification.

Each of the first columnar section 523 and the second columnar section525 of a terminal 515 is formed in a taper where the diameter of theside opposite to the first surface 3 a is enlarged from that of thefirst surface 3 a side. The end face of the first columnar section 523on the second columnar section 525 side is larger in diameter than theend face of the second columnar section 525 on the first columnarsection 523 side. At the boundary between the first columnar section 523and the second columnar section 525, a step 529 at which the firstsurface 3 a side has a diameter enlarged more than the side opposite tothe first surface 3 a is formed. In other words, the terminal 515 has athird tapered portion (first columnar section 523) in which thecross-sectional area of the side opposite to the first surface 3 a islarger than the cross-sectional area of the first surface 3 a side andhas a fourth tapered portion (second columnar section 525) whichcontinues from the third tapered portion and has a cross-sectional areaon the side opposite to the first surface 3 a larger than thecross-sectional area of the first surface 3 a side. Further, whencomparing the cross-sectional area of the third tapered portion on thefourth tapered portion side with the cross-sectional area of the fourthtapered portion on the third tapered portion side, the cross-sectionalarea of the third tapered portion on the fourth tapered portion side ismade larger. Note that, the first columnar section 523 and the secondcolumnar section 525 may have the same size and shape as each other orhave sizes and shapes different from each other.

According to such a configuration, by engagement of the step 529 withthe cover member 509 from the side by the first surface 3 a, pullout ofthe terminal 515 is suppressed.

The method for manufacturing the SAW device 501 is substantially thesame as the method for manufacturing the SAW device 1 of the aboveembodiment. Note, in the method for manufacturing the SAW device 501, awall section 519 and frame section 521 are formed by positivephotolithography in place of negative photolithography.

When a first hole portion 541 and a second hole portion 551 to be filledwith metal to form a terminal 515 are formed by positivephotolithography, in the same way as the above embodiment, a firstcolumnar section 541 and second columnar section 551 form tapered shapesdue to diffusion of light. However, the irradiated region and the notirradiated region of the light are reverse to those of the negativetype, therefore the first hole portion 541 and second hole portion 551are enlarged in their diameters in a direction reverse to that for thefirst hole portion 41 and second hole portion 51 in the aboveembodiment.

Further, due to the formation of a vibration space 517 by positivephotolithography, an inner wall 519 a and a ceiling 521 a have shapesinverse to those of the inner wall 19 a and ceiling 21 a in the firstembodiment, that is, shapes where the diameter becomes larger toward theside opposite to the first surface 3 a.

Note that, as explained above, a tapered hole can be formed by obliquelyirradiating light and so on. Therefore, it is also possible to form thefirst hole portion 541 and second hole portion 551 by negativephotolithography.

The vibration space is not limited to one formed by closing an openingof a wall section of a cover member by a lid formed separately from thewall section. For example, a vibration space may be formed by forming aresist having the same shape as that of the vibration space on thesubstrate, forming a cover member-forming layer which becomes the covermember on that, then removing the resist through a through hole providedin the cover member-forming layer.

The vibration space does not have to be formed in an arch shape.Further, when forming the vibration space in an arch shape, the arch isnot limited to one formed by chamfering the portion of the inner wall onthe ceiling side to a curved surface. For example, the arch may beformed by configuration of the entire inner wall by a planar taperedsurface. Further, the position of the boundary between the first taperedportion and the second portion from the first surface 3 a does notalways have to coincide with the position of the ceiling of thevibration space 17 from the first surface 3 a. The positions of the twomay be offset as well.

Further, the inclination angles (angles formed by the tapered portionstogether with the first surface 3 a of the piezoelectric substrate) ofthe first tapered portion and second tapered portion may be madedifferent from each other as well. For example, the first columnarsection 23 and second columnar section 25 may be formed so that theinclination angle of the first tapered portion becomes larger than theinclination angle of the second tapered portion. By making theinclination angle of the first tapered portion and the inclination angleof the second tapered portion different in this way, when force isapplied in a direction pushing against the terminal 15, the forcetransmitted to the wall section 19 can be dispersed in a broader range.

REFERENCE SIGNS LIST

1 . . . SAW device (acoustic wave device), 3 . . . piezoelectricsubstrate (substrate), 3 a . . . first surface (surface), 6 . . .comb-shaped electrode (excitation electrode), 9 . . . cover member, and15 . . . terminal.

The invention claimed is:
 1. An acoustic wave device, comprising: asubstrate configured to propagate acoustic waves; an excitationelectrode located on a surface of the substrate; a connection-useconductor located on the surface of the substrate and electricallyconnected to the excitation electrode; a terminal of with apillar-shaped located on the surface of the substrate, electricallyconnected to the connection-use electrode and comprising a first regionin the direction of height thereof with a cross-sectional area of asurface side larger than a cross-sectional area of an opposite side withrespect to the surface; and a cover member covering a side surface ofthe first region of the terminal.
 2. The acoustic wave device accordingto claim 1, wherein the terminal further comprises a tapered portion inwhich the surface side has a diameter larger than the opposite side ofthe surface.
 3. The acoustic wave device according to claim 2, whereinthe tapered portion of the terminal comprises a first tapered portion,and a second tapered portion continuing from the side of the firsttapered portion which is the surface, and a cross-sectional area of thefirst tapered portion on the second tapered portion side is smaller thanthe cross-sectional area of the second tapered portion on the firsttapered portion side.
 4. The acoustic wave device according to claim 3,wherein: the cover member comprises a wall section configured tosurround the excitation electrode when viewed from the top surface, andcomprises a lid which closes an upper side of the wall section, and adistance of a boundary between the first tapered portion and the secondtapered portion from the surface coincides with a distance of an innersurface of the lid from the surface.
 5. The acoustic wave deviceaccording to claim 4, wherein the an inner side surface of the wallsection is inclined inwardly as going away from the surface of thesubstrate.
 6. The acoustic wave device according to claim 1, wherein:the terminal further comprises a third tapered portion in which across-sectional area of a side opposite to the surface is larger than across-sectional area of the surface side, and a fourth tapered portionwhich continues from the opposite side to the surface of the thirdtapered portion surface and which has a cross-sectional area on theopposite side opposite to the surface larger than a cross-sectional areaon the surface side, and a cross-sectional area of the third taperedportion on the fourth tapered portion side is larger than across-sectional area of the fourth tapered portion on the third taperedportion side.
 7. The acoustic wave device according to claim 1, theterminal is electrically connected to the connection-use conductorthrough a connection strengthening layer formed by a material differentfrom the connection-use conductor.
 8. A circuit board, comprising: theacoustic wave device according to claim 1; and a base member on whichthe acoustic wave device is mounted through a bump touching theterminal.
 9. An acoustic wave board, comprising: a substrate configuredto propagate acoustic waves; an excitation electrode located on asurface of the substrate; a connection-use conductor located on thesurface of the substrate and electrically connected to the excitationelectrode; and a cover member in which a vibration space on theexcitation electrode and a hole on the connection-use conductor areformed; wherein the hole comprises a first region in the direction ofheight thereof with a cross-sectional area of a surface side larger thana cross-sectional area of an opposite side with respect to the surface.10. The acoustic wave board according to claim 9, wherein the holecomprises a tapered portion in which the surface side has a diameterlarger than the opposite side of the surface.
 11. An acoustic wavedevice comprising: the acoustic wave board according to claim 9; and aterminal located in the hole and electrically connected to theconnection-use conductor.
 12. An acoustic wave board, comprising: asubstrate configured to propagate acoustic waves; an excitationelectrode located on a surface of the substrate; a connection-useconductor located on the surface of the substrate and electricallyconnected to the excitation electrode; and a cover member in which avibration space on the excitation electrode and a hole on theconnection-use conductor are formed; wherein the hole comprises a firstregion in the direction of height thereof with a cross-sectional area ofa surface side smaller than a cross-sectional area of an opposite sidewith respect to the surface.
 13. The acoustic wave board according toclaim 12, wherein the hole comprises a tapered portion in which thesurface side has a diameter smaller than the opposite side of thesurface.
 14. The acoustic wave board according to claim 12, wherein aninner periphery of the hole at an end portion of the surface side issmaller than outer periphery of the connection-use conductor.
 15. Theacoustic wave board according to claim 12, wherein the cover membercomprises a wall section configured to surround the excitation electrodewhen viewed from the top surface, and a lid which closes an upper sideof the wall section, and an inner side surface of the wall section isinclined outwardly as going away from the surface of the substrate. 16.An acoustic wave device comprising: the acoustic wave board according toclaim 12; and a terminal located in the hole and electrically connectedto the connection-use conductor.